1. Field of the Invention
The present invention is generally related to guide pins for a nuclear reactor fuel assembly and more particularly to the replacement of existing guide pins.
2. General Background
In commercial nuclear reactors fuel guide pins extend down from the upper core plate into guide tubes in the fuel assemblies. This aids in maintaining proper alignment of the fuel assemblies with the pressure vessel so that the control rods operate properly. During initial construction of the reactor each guide pin is inserted into a bore in the upper core plate from the bottom of the plate and threadably secured with a nut at the top of the core plate. The nut is then welded to the pin to prevent loosening during service. After construction is completed and operation begun, fuel guide pins may need to be replaced due to a defect or the fuel guide pin becoming bent. A problem encountered in replacing fuel guide pins is that the top of the upper core plate is very difficult to access. This makes removal of the nut from the top of the core plate very difficult and time consuming.